Hi Eli, Could you add a regression test from the testcase in the PR, to verify that the load is optimized out?
Thanks, Dan On Feb 12, 2008, at 4:08 AM, Eli Friedman wrote: > Author: efriedma > Date: Tue Feb 12 06:08:14 2008 > New Revision: 47006 > > URL: http://llvm.org/viewvc/llvm-project?rev=47006&view=rev > Log: > Fix for bug 1996: optimize out loads of undef. This code basically > just > checks for a malloc/alloca immediately followed by a load. > > Modified: > llvm/trunk/lib/Transforms/Scalar/GVN.cpp > > Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp > URL: > http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVN.cpp?rev=47006&r1=47005&r2=47006&view=diff > > = > = > = > = > = > = > = > = > ====================================================================== > --- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original) > +++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Tue Feb 12 06:08:14 2008 > @@ -1010,7 +1010,34 @@ > dep = MD.getDependency(L, dep); > } > } > - > + > + if (dep != MemoryDependenceAnalysis::None && > + dep != MemoryDependenceAnalysis::NonLocal && > + isa<AllocationInst>(dep)) { > + // Check that this load is actually from the > + // allocation we found > + Value* v = L->getOperand(0); > + while (true) { > + if (BitCastInst *BC = dyn_cast<BitCastInst>(v)) > + v = BC->getOperand(0); > + else if (GetElementPtrInst *GEP = > dyn_cast<GetElementPtrInst>(v)) > + v = GEP->getOperand(0); > + else > + break; > + } > + if (v == dep) { > + // If this load depends directly on an allocation, there isn't > + // anything stored there; therefore, we can optimize this load > + // to undef. > + MD.removeInstruction(L); > + > + L->replaceAllUsesWith(UndefValue::get(L->getType())); > + toErase.push_back(L); > + deletedLoad = true; > + NumGVNLoad++; > + } > + } > + > if (!deletedLoad) > last = L; > > > > _______________________________________________ > llvm-commits mailing list > llvm-commits@cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits _______________________________________________ llvm-commits mailing list llvm-commits@cs.uiuc.edu http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
